In the past years, the telecommunications industry has been solving several inter-related problems in the converged (both mobile and fixed) networks:
1. Establishment of a user session in a managed IP network;
2. Policy-based admission control; and
3. Policy enforcement.
The first item above, user session establishment, addresses signaling between an end point (i.e., user equipment terminal) and the network in order to establish an end-to-end session (such as a Voice-over-IP telephone call or a conference call, or an IP TV session). Policy-based admission control refers to the process triggered during session establishment, in which the network itself is determining whether there are sufficient resources (i.e., bandwidth) in the network to admit the relevant IP flows (defined by the quintuple that contains the originating and terminating IP addresses and originating and terminating port numbers along with the protocol identifier); if such resources are found and the request is authorized as legitimate, the network instructs the appropriate devices at its edges to admit the authorized flows (and, in the most general case, ensure that they conform to specific policies). Policy enforcement deals with actual admission of the traffic from end points. The IP Multimedia Subsystem (IMS), ETSI TS 123 002 V7.1.0 (2006-03), Digital cellular telecommunications system (Phase 2+); Universal Mobile Telecommunications System (UMTS); Network Architecture and ETSI TS 123 228 V7.3.0, (2006-03), Digital cellular telecommunications system (Phase 2+); Universal Mobile Telecommunications System (UMTS); IP Multimedia Subsystem (IMS); Stage 2, has defined an architecture and a set of standards that support the implementation of the above functions. Subsequently, this has been further elaborated within the framework of a more general architecture presently developed by ITU-T within the framework of Resource Admission and Control Functions known as ITU-T New Draft Recommendation Y.2111 (formerly Y.RACF), Resource and Admission Control Functions in Next Generation Networks.